Thin profile user interface device and method providing localized haptic response

ABSTRACT

Electromechanical polymer (EMP) actuators are used to create haptic effects on a user interface deface, such as a keyboard. The keys of the keyboard may be embossed in a top layer to provide better key definition and to house the EMP actuator. Specifically, an EMP actuator is housed inside an embossed graphic layer that covers a key of the keyboard. Such a keyboard has a significant user interface value. For example, the embossed key provides the tactile effect of the presence of a key with edges, while allowing for the localized control of haptic vibrations. For such applications, an EMP transducer provides high strains, vibrations or both under control of an electric field. Furthermore, the EMP transducer can generate strong vibrations. When the frequency of the vibrations falls within the acoustic range, the EMP transducer can generate audible sound, thereby functioning as an audio speaker.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Non-Provisionalapplication Ser. No. 13/735,804 filed Jan. 7, 2013, entitled “ThinProfile User Interface Device and Method Providing Localized HapticResponse,” and PCT Application Serial No. PCT/US13/71062 filed Feb. 12,2014, which are incorporated herein by reference in their entirety forall purposes.

The present patent application is related to U.S. Provisional PatentApplication (“Copending Provisional Application”), Ser. No. 61/679,641,filed Aug. 3, 2012, entitled “Electromechanical Polymer Actuators forHaptic Feedback,” and U.S. Patent Applications (“CopendingApplications”) (i) Ser. No. 13/683,980, entitled “Haptic System withLocalized Response,” filed Nov. 21, 2012, and (ii) Ser. No. 13/683,928,entitled “EMP Actuators for Deformable Surface and KeyboardApplication,” also filed on Nov. 21, 2012. The disclosures of theCopending Provisional Application and the Copending Applications arehereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to using transducers based onelectromechanical polymers (EMP) layers; in particular, the presentinvention relates to use of such transducers to provide haptic responsein keys of a thin profile keyboard.

2. Discussion of the Related Art

Transducers are devices that transform one form of energy to anotherform of energy. For example, a piezoelectric transducer transformsmechanical pressure into an electrical voltage. Thus, a user may use thepiezoelectric transducer as a sensor of the mechanical pressure bymeasuring the output electrical voltage. Alternatively, some smartmaterials (e.g., piezoceramics and dielectric elastomers (DEAP)) deformproportionally in response to an electric field. An actuator maytherefore be formed out of a transducer based on such a smart material.Actuation devices based on these smart materials do not requireconventional gears, motors, and cables to enable precise articulationand control. These materials also have the advantage of being able toexactly replicate both the frequency and the magnitude of the inputwaveform in the output response, with switching time in the millisecondrange.

For a smart material that has an elastic modulus Y, thickness t, widthw, and electromechanical response (strain in plane direction) S₁, theoutput vibration energy UV is given by the equation:

UV=½YtwS₁ ²  (1)

DEAP elastomers are generally soft, having elastic moduli of about 1MPa. Thus, a freestanding, high-quality DEAP film that is 20 micrometers(μm) thick or less is difficult to make. Also, a DEAP film provides areasonable electromechanical response only when an electric field of 50MV/m (V/μm) or greater is applied. Thus, a DEAP type actuator typicallyrequires a driving voltage of 1,000 volts or more. Similarly, a DEAPtype sensor typically requires a charging voltage of 1,000 volts ormore. In a handheld consumer electronic device, whether as a sensor oras an actuator, such a high voltage poses safety and cost concerns.Furthermore, a DEAP elastomer has a low elastic modulus. As a result, toachieve the strong electrical signal output needed for a handheld deviceapplication requires too thick a film. The article, “Combined DrivingSensing Circuitry for Dielectric Elastomer Actuators in MobileApplications,” by M. Matsek et al., published in Electroactive PolymerActuators and Devices (EAPAD) 2011, Proc. Of SPIE vol. 7975, 797612,discloses providing sensor functions in dielectric elastomer stackactuators (DESA). U.S. Pat. No. 8,222,799 to Polyakov, entitled “SurfaceDeformation Electroactive Polymer Transducers,” also discloses sensorfunctions in dielectric elastomers.

Unlike a DEAP elastomer, a piezoceramic material can provide therequired force output under low electric voltage. Piezoelectricmaterials are crystalline materials that become electrically chargedunder mechanical stress. Converse to the piezoelectric effect isdimensional change as a result of imposition of an electric field. Incertain piezoelectric materials, such as lead zirconate titanate (PZT),the electric field-induced dimensional change can be up to 0.1%. Suchpiezoelectric effect occurs only in certain crystalline materials havinga special type of crystal symmetry. For example, of the thirty-twoclasses of crystals, twenty-one classes are non-centrosymmetric (i.e.,not having a center of symmetry), and of these twenty-one classes,twenty classes exhibit direct piezoelectricity. Examples ofpiezoelectric materials include quartz, certain ceramic materials,biological matter such as bone, DNA and various proteins, polymers suchas polyvinylidene fluoride (PVDF) and polyvinylidenefluoride-co-trifluoroethylene [P(VDF-TrFE)]. For further information,see, for example, the article “Piezoelectric Transducer Materials”, byH. JAFFE and D. A. BERLINCOURT, published on pages 1372-1386 ofPROCEEDINGS OF THE IEEE, VOL. 53, No. 10, OCTOBER, 1965.

The strain of a piezoelectric device is linearly proportional to theapplied electric field E:

S ₁ ≠E  (2)

As illustrated in equation (2), when used in an actuator device, apiezoelectric material generates a negative strain (i.e., shortens)under a negative polarity electric field, and a positive strain (i.e.,elongates) under a positive electric field. However, piezoceramicmaterials are generally too brittle to withstand a shock load, such asthat encountered when the device is dropped.

Piezoceramics and dielectric elastomers change capacitance in responseto a mechanical deformation, and thus may be used as pressure sensors.However, as mentioned above, DEAP elastomers are generally soft, havingelastic moduli of about 1 MPa. Thus, a freestanding, high-quality DEAPfilm that is 20 micrometers (μm) thick or less is difficult to make.

Unlike the piezoelectric materials that require a special type ofcrystal symmetry, some materials exhibit electrostrictive behavior, suchas found in both amorphous (non-crystalline) and crystalline materials.“Electrostrictive” or “electrostrictor” refers to a strain behavior of amaterial under an electric field that is quadratically proportional tothe electric field, as defined in equation (3)

S ₁ ˜E ²  (3)

Therefore, in contrast to a piezoelectric material, an electrostrictiveactuator always generates positive strain, even under a negativepolarity electric field (i.e., the electrostrictive actuator onlyelongates in the direction perpendicular to the imposed field), with anamplitude that is determined by the magnitude of the electric field andregardless of the polarity of the electric field. A description of someelectrostrictive materials and their behavior may be found, for example,in the articles (a) “Giant Electrostriction and relaxor ferroelectricbehavior in electron-irradiated poly(vinylidenefluoride-trifluoroethylene) copolymer”, by Q. M. Zhang, et al, publishedin Science 280:2101 (1998); (b) “High electromechanical responses interpolymer of poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene)”, by F. Xia et al,published in Advanced Materials, 14:1574 (2002). These materials arebased on electromechanical polymers. Some further examples of EMPs aredescribed, for example, in U.S. Pat. Nos. 6,423,412, 6,605,246, and6,787,238. Other examples include the EMPs whose compositions disclosedin pending U.S. patent application Ser. No. 13/384,196, filed on Jul.15, 2009, and the EMPs which are blends of the P(VDF-TrFE) copolymerwith the EMPs disclosed in the aforementioned U.S. Patents.

To achieve a substantially linear response and mechanical strains of,say, up to four (4) percent, in a longitudinal or transverse direction,the electrorestrictive EMPs discussed above requires an electric fieldintensity between 50 to 100 MV/m. In the prior art, to provide adequatemechanical strength and flexibility, the polymer films are at least 20μm thick. As a result, an actuator based on such an electrostrictive EMPrequires an input voltage of about 2000 volts. Such a voltage istypically not available in a mobile device.

Polyvinylidene difluoride (PVDF) andpoly[(vinylidenefluoride-co-trifluoroethylene (P(VDF-TrFE)) arewell-known ferroelectric sensor materials. However, these materialssuffer from low strain, and thus perform poorly for many applications,such as keys on a keyboard.

FIG. 1 illustrates the basics of an exemplary EMP actuator 100 creatingmechanical motion in response to an electrical stimulation. As shown inFIG. 1, EMP actuator 100 includes EMP layer 102, which may be itselfconsists of a number of EMP layers, is bonded to substrate 103.Substrate layer 103 is made of a thin, flexible material that is notcompliant the longitudinal direction. During a quiescent state, i.e.,without an electrical potential imposed across EMP layer 102, EMPactuator 100 is unstressed (FIG. 1a ). When a DC electrical potential(i.e., 0 Hz) is imposed across EMP layer 102, EMP layer 102 elongates.As substrate 102 is not sensitive to the electrical potential, a largemechanical stress causes EMP actuator 100 to buckle, as shown in FIG.1(b). With a non-zero driving frequency, vibrations may be created atdifferent frequencies.

One area that EMPs find application is haptics. In this context, theterm “haptics” refers to tactile user input actions. In a conventionalkeyboard, the mechanical, spring-loaded action of a pressed key and theassociated audio “click” are haptic responses to the touch typist that akey has been successfully depressed. Similarly, a haptics-enabled touchscreen may generate an immediate haptic feedback vibration when the keyis activated by user input. The feedback vibration makes the virtualelement displayed on the touch screen more physical and more realistic.In a portable device (e.g., a mobile telephone), a haptic feedbackaction can reduce both user input errors and stress, allow a higherinput speed, and enable new forms of bi-directionally interactions,Haptics is particularly effective for keyboards that are used in noisyor visually distracting environments (e.g., a battlefield or a gamingenvironment). Haptics can reduce input error rates and improve responsespeed.

Recently proposed high-definition (HD) haptics may provide significantlymore tactile information to a user, such as texture, speed, weight,hardness, and damping. HD haptics uses frequencies that may be variedbetween 50 Hz to 400 Hz to convey complex information, and to provide aricher, more useful and more accurate haptic response. Over thisfrequency range, a user can distinguish feedback forces of differentfrequencies and amplitudes. The feedback vibration is expected to becontrolled by software. For a user to experience a strong feedbacksensation, HD haptics in this frequency range, switching times (i.e.,rise and fall time) between frequencies of 40 milliseconds (ms) or lessare required. The ability to provide such HD feedback vibrations in the50 Hz to 400 Hz band, however, is not currently available. In the priorart, a typical device having basic haptics has an output magnitude thatvaries with the frequency of the driving signal. Specifically, thetypical device provides a greater output magnitude at a higher frequencyfrom the same input driving amplitude. For example, if a haptic drivingsignal includes two equal-magnitude sine waves at two distinctfrequencies, the output vibration would be a superposition of two sinewaves of different magnitudes, with the magnitudes being directlyproportional to the respective frequencies. Such a haptic response isnot satisfactory. Therefore, a compact, low-cost, low-driving voltage,and robust HD haptics actuation device is needed.

Haptic responses need not be limited to 50 Hz to 400 Hz vibrations. Atlower frequency, a mechanical pressure response may be appropriate.Vibrations in the acoustic range can be made audible. A haptic responsethat can be delivered in more than one mode of sensation (e.g.,mechanical pressure, vibration, or audible sound) is termed“multimodal.”

Recently, the consumer electronics industry has been demanding very thinprofile keyboards (e.g., 2-3 mm thick). For example, MicrosoftCorporation introduced for its Surface tablet computer a keyboard whichalso serve as a protective cover of the tablet computer. FIG. 2 shows aside view of prior art thin profile keyboard 200. As shown in FIG. 2,keyboard 200 includes substrate or base layer 201, force-sensingresistor (FSR) layer 202 and cover layer 203. Base layer 201 providesprotection and mechanical support for keyboard 200. FSR layer 202 is asensing layer which is made of a material which resistance changes withan applied mechanical force on its surface (e.g., the pressure appliedby a human finger, as illustrated in FIG. 2). Cover layer 203 providesprotection to FSR layer 202. Cover layer 203 is thus made of a durablematerial. In addition, as the force of the user's finger is transmittedby cover layer 203 to FSR layer 202, cover layer 203 is made of aflexible material. Typically, base layer 201 is the most rigid layer ofkeyboard 200. However, without haptic feedback, such thin profilekeyboards are not satisfactory to most users.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, electromechanicalpolymer (EMP) actuators are used to create haptic effects on a mobiledevice's mechanical interfaces (e.g., keys of a keyboard). In someembodiments, the keys of the keyboard are embossed in a top layer toprovide better key definition and to house the EMP actuator.Specifically, an EMP actuator is housed inside an embossed graphic layerthat covers a key of the keyboard. The present invention is ofsignificant user interface value. For example, the embossed key providesthe tactile effect of the presence of a key with edges, while allowingfor the localized control of haptic vibrations. For such applications,an EMP transducer provides high strains, vibrations or both undercontrol of an electric field. Furthermore, the EMP transducer cangenerate strong vibrations. When the frequency of the vibrations fallswithin the acoustic range, the EMP transducer can generate audiblesound, thereby functioning as an audio speaker. Thus, the EMP actuatorof the present invention can provide a multimodal haptic response (e.g.,generating deformable surface, vibration, or audible sound, asappropriate). In addition, the EMP transducer can also serve as a touchsensor, as a mechanical pressure applied on the EMP transducer caninduce a measurable electrical voltage output. Therefore, the EMPtransducer may serve as both a sensor and an actuator.

The EMP layer is charged by the excitation signal. The excitation signalmay have a frequency in a frequency range within the human acousticrange. In response to the excitation signal, the associated EMP actuatorvibrates at substantially the frequency of the excitation signal. Thefrequency range may be between 0 Hz (i.e., DC) to 10,000 Hz, dependingon the EMP actuator's application. When the EMP actuator is used toprovide a haptic feedback, the frequency may be in the range of 50 Hz to400 Hz; and when the EMP actuator is used to provide certain acousticfunctions, the frequency can be in the range of 400 Hz to 10,000 Hz. Thevibration of the EMP actuator may provide an audible sound. The EMPactuator disclosed herein may have a response latency relative to theexcitation signal of less than 40 milliseconds. In addition, the EMPactuator may have a decay time of less than 40 milliseconds. The EMPlayer may have an elastic modulus greater than 500 MPa at 25° C. and anelectromechanical strain greater than 1%, when experiencing an electricfield of greater than 100 MV/m.

Unlike current haptics system which typically vibrates the entireelectrical device, which is often rigid, the EMP actuator-enabledhaptics can vibrate directly under the point of contact (e.g., a user'sfinger). In one embodiment, an array or grid of EMP actuators areprovided, in which only the actuator under the touch is selectivelyactivated, thereby providing a “localized” haptics feedback. When theEMP actuators are arranged in sufficiently close vicinity of each other,the haptic system may take advantage of haptic responses that aresuperimposed for constructive interference. In some embodiments, thesubstrate may vibrate in concert with the EMP actuators.

When a specific key is pressed by a user, an excitation signal may beprovided to cause the associated EMP actuator to vibrate, so as toconfirm to the user that the user's typing action has been detected.

According to one embodiment of the present invention, the EMP actuatorof the haptic system may be activated by a high frequency signal havingone or more frequency components in the range of 400 Hz to 10,000 Hz.The high frequency vibration of the EMP actuator (or the EMP actuatortogether with the substrate) can generate an audible acoustic signal asa feedback response.

The present invention is better understood upon consideration of thedetailed description below in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the basics of an EMP actuator creating mechanicalmotion in response to an electrical stimulation.

FIG. 2 shows a side view of prior art thin profile keyboard 200.

FIG. 3 shows a side view of keyboard 300 having an electromechanicalpolymer (EMP) actuator included with each key or surface, in accordancewith one embodiment of the present invention.

FIG. 4 shows some examples of the shapes of EMP actuators (e.g., EMPactuators 310) may be made into, as seen from above.

FIG. 5 shows EMP actuator 500, having a shape that is suitable for usein keys and surfaces.

FIG. 6 shows some exemplary cushion shapes, in accordance with oneembodiment of the present invention.

FIG. 7 shows schematically embossed key 700 of a keyboard in which EMPactuator 701 is attached to the embossed area 702 of cover layer 705, inaccordance with one embodiment of the present invention.

FIG. 8 shows four types of standoffs that can be used in conjunctionwith embossed key 700.

FIG. 9(a) shows embossed key 900, according to another embodiment of thepresent invention.

FIG. 9(b) shows embossed key 920, according to another embodiment of thepresent invention.

FIGS. 10(a), (b) and (c) show different configurations of mobilecomputer 1000, which includes 2-sided keyboard 1002 and cover/stand1003, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to one embodiment of the present invention, haptic feedbackresponse is provided in a mechanical interface, such as a thin profilekeyboard, using electromechanical polymer (EMP) actuators. Throughoutthis detailed description, keys on a keyboard are used to illustrate thepresent invention without an intention to so limit. In fact, the presentinvention is applicable to other mechanical interfaces at which alocalized haptic response is desired.

FIG. 3 shows a side view of keyboard 300 having an EMP actuator includedwith each key or surface, in accordance with one embodiment of thepresent invention. As shown in FIG. 3, keyboard 300 includes base layer301, force-sensing resistor (FSR) layer 302, spacer layer 304, includinga number of cavities for accommodating numerous EMP actuators 310, andcover layer 305. EMP actuators 310 are attached to cover layer 305 andare each separated from FSR layer 302 by a cushion 303. Base layer 301and FSR layer 302 perform like functions as base layer 201 and FSR layer202 of FIG. 2. Specifically, base layer 301 provides protection andmechanical support for keyboard 300. FSR layer 302 is the sensing layerand is made of a material which resistance changes with an appliedmechanical force on its surface (e.g., the pressure applied by a humanfinger, as illustrated in FIG. 3). EMP actuators 310 are each alignedvertically with an active sensing area of FSR layer 302 (“FSR sensor”).The portions of FSR layer 302 outside of the FSR sensors are inactiveareas where support structures and wiring are provided. Spacer layer304, having a thickness in the range of 0.2 mm to 0.5 mm, for example,is provided above the inactive areas of FSR layer 302. Cover layer 305,which is preferably made of a durable, flexible material, protects FSRlayer 302 and transmits any force impressed, for example, by a user'sfinger, to FSR layer 302. When a user touches a key, the pressure of thetouch is transmitted to the corresponding FSR sensor, which provides anelectrical signal to a controller. In response, the controller activatesthe corresponding EMP actuator to provide a haptic feedback response.

As EMP actuators 310 are made from a polymer material, each of EMPactuators 310 may be made into any suitable shape. FIG. 4 shows someexamples of the shapes EMP actuators 310 may be made into, as seen fromabove. In particular, FIG. 5 shows EMP actuator 500, which has a shapethat is suitable for use in keys and surfaces. As shown in FIG. 5, EMPactuator 500 has a footprint that is, for example, 14 mm by 14 mm,including a 14 mm by 12 mm active area. An exemplary capacitance for EMPactuator 500 may be about 250 nanofarad of capacitance. As EMP actuators310 are attached to the back side of cover layer 305, cover layer 305together with the EMP actuators 310 create a vibration structure. Thatis, an additional passive layer (e.g., substrate layer 103 of FIG. 1) isnot necessary for creating a vibration structure. When an EMP actuatoris actuated, its vibration is transmitted through cover layer 305 toprovide the haptic feedback to the user.

As seen from FIG. 3, cushion 303 is provided between each of EMPactuators 310 and the corresponding FSR sensor. The thickness of thecushions are specifically designed to be slightly less than the distancebetween the EMP actuator on which it is attached and the correspondingactive area of FSR layer 302, so as to avoid imposing a force on the FSRsensor when there is no force on the corresponding area of cover layer305. The cushion reduces attenuation of the haptic feedback when a userpushes hard on a key. A properly designed cushion reduces theattenuation of the haptic feedback response. FIG. 6 shows some exemplarycushion shapes, in accordance with one embodiment of the presentinvention. As shown in FIG. 6, examples (a)-(b) are in the forms ofcircular or rectangular cylinders with an annular 1 mm thick crosssections, and example (c) has four posts each with a rectangular crosssection of about 1 mm in width or breadth. Each cushion may preferablyhave a hardness between 20 A to 30 A. The internal diameter of example(a) is preferably roughly 10 mm.

According to one embodiment of the present invention, the EMP actuatoris attached to a raised or embossed area of the cover layer. Such anembossing structure may increase the strength of the haptic feedback byan EMP actuator. FIG. 7 shows schematically embossed key 700 of akeyboard in which EMP transducer 701 is attached to the embossed area702 of cover layer 705, in accordance with one embodiment of the presentinvention. As shown in FIG. 7, embossed key 700 includes EMP transducer701, which is attached to embossed area 702, standoff or cushion 703,and FSR sensor 706 embedded in mechanical ground 704. In FIG. 7,mechanical ground 704 embeds FSR sensor 706; however, other thin filmtype sensors underneath standoffs. Cushion 703 may have any of the formsshown in FIG. 8 (i.e., annular with a circular cross section, in twoparallel strips, in four cubes, annular with a rectangular crosssection) or may be provided as a solid piece. Alternatively, EMPtransducer 701 may serve as both an actuator and an electromechanicalsensor. Standoff or cushion 703 limits the distance of mechanical travelbetween EMP transducer 701 and mechanical ground 704 when embossed key700 is loaded by a user's finger. The thickness (t) of standoff 703determines the distance of mechanical travel experienced by embossed key700 when loaded by a user's finger. Therefore, the thickness allows fortuning of the mechanical travel. Furthermore, when the user presses onembossed key 700, standoff 703 captures the pressure on EMP transducer701, such that the haptic vibration is not significantly damped. Theheight of the embossing may be around 0.20.4 mm, for example.

The haptic response can be isolated to the embossed structure (i.e.,embossed key 700) only, thus enforcing the ability to provide alocalized haptics response to only the key of interest. In this way,haptic vibrations occurring at a key of interest are not felt at aneighboring key. Thus, embossed key 700 has the advantage ofincorporating both the kinesthetic presence of a geometrically definedkey, as well as providing a haptic vibration response, without undulyadding to the thickness of the key. FIG. 8 shows four types of standoffsthat can be used in embossed key 700. Standoff 703 transfers force fromthe embossing structure to the thin film force sensor, and does notsignificantly attenuate vibration from the EMP sensor. EMP transducer701 may vibrate at different frequencies or at different amplitudesunder different conditions.

An embossed key is much more clearly defined to the user, facilitatingthe user's determination of the exact location of the key with his/hertactile feeling. In addition, the haptic feedback response (e.g.,vibration) is much stronger in the embossed structure.

FIG. 9(a) shows embossed key 900, according to another embodiment of thepresent invention. As shown in FIG. 9(a), EMP actuator 905 is attachedto an underside of an embossed area 907 of cover layer 901 of embossedkey 900 in a thin profile keyboard. EMP actuator 902 is separated bycushion 904 from FSR sensor 905 which is embedded in a FSR layerprovided above substrate or base 903. Alternatively, as shown in FIG.9(b), some embodiments need not include a physical cushion structureunderneath the EMP layer. Thus, FIG. 9(b) shows embossed key 920,according to another embodiment of the present invention. As shown inFIG. 9(b), EMP actuator 925 is attached to an underside of an embossedarea 907 of cover layer 921 of embossed key 920 in a thin profilekeyboard. Rather than by a cushion, EMP actuator 925 is separated by airgap or space 924 from FSR sensor 922, which is embedded in a FSR layerprovided above substrate or base 923. In still other embodiments,neither cushion 904 nor space 924 is provided, i.e., the EMP actuator ofthe EMP actuator directly contacts an FSR sensor. Such an embodiment mayprovide a keyboard of even thinner profile.

Because of their thin profiles, the keyboards of the present inventionmay be used with many types of mobile devices, such as tablet computers.Such a keyboard may be used for other functions also (e.g., protectivecovering). FIGS. 10(a), (b) and (c) show different configurations ofmobile computer 1000, which includes 2-sided keyboard 1002, inaccordance with one embodiment of the present invention. As shown inthese figures, mobile computer 1000 includes tablet device 1001, 2-sidedkeyboard 1002 and protective cover 1003. Protective layer 1003 and2-sided keyboard 1002 are attached along one side of table device 1001.Protective cover 1003 may be folded in such a way to serve as a stand toprop up tablet device 1001 in the manner shown in FIGS. 10(a) and 10(b).In these configurations, protective cover 1003 serves as a stand fortablet device 1001. To serve in this function, protective cover 1003 maybe provided a crease or is hinged to allow it to be folded into a stand.2-sided keyboard 1002 is a thin pad that has keys of the presentinvention provided on both sides, such that each side can be used byitself as an independent keyboard. In the configurations of FIGS. 10(a)and 10(b), the user can view the entire surface of tablet device 1001 ata favorable angle. Either side of 2-sided keyboard 1002 may be used forinput purpose. In FIG. 10(c), protective cover 1003 is configured to layflat against tablet device 1001 to provide protection on the back side,while 2-sided keyboard 1002 is rests flat against a lower half surfaceof tablet device 1001. In this configuration, a portion of tablet device1001 is covered by 2-sided keyboard 1002. However, mobile computer 1000may be used in the conventional tablet fashion, allowing data input tobe made through the keys of 2-sided keyboard 1002 on the side facingaway from the display surface of tablet device 1001.

The electromechanical polymer (EMP) transducers suitable for the presentinvention disclosed herein are numerous, including ferroelectric,dielectric elastomer, piezoelectric and electro-restrictive materials.

Some examples of the electromechanically active polymers incorporated inthe EMP transducers of the present invention include P(VDF-TrFE)modified by either high energy density electron irradiation or bycopolymerization with a third monomer. Under such a modification, theEMP loses its piezoelectric and ferroelectric behaviors and become an“electrostrictive” or “relaxor ferroelectric” material.

An electromechanical polymer (EMP) transducer typically includes a largenumber of EMP active layers (e.g., 1-1000 or more layers) and electrodesbonded to each layer thereto. The EMP active layers may be configured asa stack, bonded to each other by an adhesive or by thermal lamination,for example, to achieve a cumulative force effect. The electrodes may bearranged to connect multiple active layers in parallel. With the EMPactive layer each being less than 10 microns thick, the EMP actuatorsmay be actuated at a low driving voltage (e.g., 300 volts or less;preferably, 150 volts or less) suitable to be powered by a wide varietyof consumer electronic devices, such as mobile telephones, laptops,ultrabooks, and tablets.

EMP layers of a EMP transducers used in the present invention may bepreprocessed (e.g., uniaxially or biaxially stretched, conventionally orotherwise, or having electrodes formed thereon) to condition the EMPlayer's electromechanical response to an applied external field. Abiaxially stretched actuator can deform in all directions in the planeof the axes of stretching. When the FSR layer of a key signals that thekey is pressed by a user, an excitation signal is provided by thekeyboard controller to cause the associated EMP actuator to vibrate, asa haptics response to confirm to the user that the user's typing actionhas been detected.

The electrodes of any EMP transducers discussed herein may be formedusing any suitable electrically conductive materials, such astransparent conducting materials (e.g., indium tin oxide (ITO) ortransparent conducting composites, such as indium tin oxidenanoparticles embedded in a polymer matrix). Other suitable conductivematerials include carbon nanotubes, graphenes, and conducting polymers.The electrodes may also be formed by vacuum deposition or sputteringusing metals and metal alloys (e.g., aluminum, silver, gold, orplatinum). Nanowires that are not visible over a graphical display layermay also be used, such as silver nanowires, copper nanowires, and alloynanowires with diameter less than 100 nm.

The present invention may be used to provide keyboards or other userinterface devices in consumer electronics, which continue to becomesmaller and thinner. Low-profile, thin keyboards are desired for usewith many information processing devices (e.g. tablet computers,ultrabook and MacBook Air). Because the EMP transducers of the presentinvention can be made very thin, according to one embodiment of thepresent invention, a keyboard based on EMP transducers may be providedwhich includes physical key movements in the manner of a conventionalkeyboard.

A haptic response may be provided as confirmation of receipt of theuser's key activation in the user's typing. In this regard, the EMPactuators may replace the spring mechanism in a classical keyboard,enabling a low-profile thin keyboard, while still providing thedesirable key travel distance in a conventional keyboard that a userexpects.

The EMP transducer can also serve as a force or pressure sensor byitself. Pressing an EMP transducer generates a voltage across thetransducer, which may be used in lieu of a conventional force transducer(e.g., the FSR sensor). In other words, the EMP transducer may serve asboth the actuator and the sensor without requiring an additionalconventional transducer.

The EMPs suitable for use in components (e.g., EMP actuators employed inhaptic substrates and haptic devices disclosed herein) typically showvery high strain of about 1% or more under an electric field gradient of100 megavolts per meter or greater. (Strain is measured as the change inlength of an EMP layer as a percentage of the quiescent length.) The EMPlayers also may show elastic modulus of about 500 MPa or more at 25° C.,a mechanical vibrational energy density of 0.1 J/cm³ or more, adielectric loss of about 5% or less, a dielectric constant of about 20or more, an operating temperature of about −20° C. to about 50° C., anda response time of less than about 40 millisecond.

Suitable electrostrictive polymers for EMP layers 140 include irradiatedcopolymers and semi-crystalline terpolymers, such as those disclosed inU.S. Pat. Nos. 6,423,412, 6,605,246, and 6,787,238. Suitable irradiatedcopolymers may include high energy electron irradiatedP(VDF_(x)-TrFE_(1-x) copolymers, where the value of x may vary between0.5 to 0.75. Other suitable copolymers may include copolymers ofP(VDF_(1-x)-CTFE_(x)) or P(VDF_(1-x)-HFP_(x)), where the value of x isin the range between 0.03 and 0.15 (in molar). Suitable terpolymers thatmay have the general form of P(VDF_(x)-2nd monomer_(y)-3rdmonomer_(1-x-y)), where the value of x may be in the range between 0.5and 0.75, and the value of y may be in the range between 0.2 and 0.45.Other suitable terpolymers may include P(VDF_(x)-TrFE_(y)-CFE_(1-x-y))(VDF: vinylidene fluoride, CFE: chlorofluoroethylene, where x and y aremonomer content in molar), P(VDF_(x)-TrFE_(y)-CTFE_(1-x-y)) (CTFE:chlorotrifluoroethylene), poly(vinylidenefluoride-trifluoroethylene-vinylidene chloride)(P(VDF-TrFE-VC)), where xand y are as above; poly(vinylidenefluoride-tetrafluoroethylene-chlorotrifluoroethylene)(P(VDF-TFE-CTFE)),poly(vinylidene fluoride-trifluoroethylene-hexafluoropropylene),poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene),poly(vinylidene fluoride trifluoroethylene-tetrafluoroethylene),poly(vinylidene fluoride tetrafluoroethylene tetrafluoroethylene),poly(vinylidene fluoride-tri fluoroethylene-vinyl fluoride),poly(vinylideneflouride-tetrafluoroethylene-vinyl fluoride),poly(vinylidene fluoride-trifluoroethyl eneperfluoro(methyl vinylether)), poly(vinylidene fluoride-tetrafluoroethylene-perfluoro (methylvinyl ether)), poly(vinylidenefluoride-trifluoroethylene-bromotrifluoroethylene, polyvinylidene),poly(vinylidene fluoride-tetrafluoroethylene-chlorofluoroethylene),poly(vinylidene fluoride-trifluoroethylene-vinylidene chloride), andpoly(vinylidene fluoride tetrafluoroethylene vinylidene chloride),

Furthermore, a suitable EMP may be in the form of a polymer blend.Examples of polymer blends include of polymer blends of the terpolymerdescribed above with any other polymers. One example includes the blendof P(VDF-TrFE-CFE) with P(VDF-TrFE) or blend of P(VDF-TrFE-CTFE) withP(VDF-TrFE). Other examples of suitable polymer blends include a blendof P(VDF-TrFE-CFE) with PVDF or a blend of P(VDF-TrFE-CTFE) with PVDF.Irradiated P(VDF-TrFE) EMP may be prepared using polymeric material thatis itself already a polymer blend before irradiation.

According to one embodiment of the present invention, to form a EMPlayer, P (VDF-TrFE-CFE) polymer powder was dissolved in N,N-dimethylformamide (DMF) solvent at 5 wt. % concentration. The solutionwas then filtered and cast onto a glass slide to produce a 30 μm thickfilm. The film was then uniaxially stretched by 700% (i.e., the finalfilm length equals to 700% of the cast film length), resulting in 5 μmthick film. The stretched 5 μm thick film was further annealed in aforced air oven at 110° C. for two hours. FIG. 1 shows storage modulusof the resulting stretched film, as measured using a dynamic mechanicalanalyzer (e.g., DMA, TA DMA 2980 instrument) at 1 Hz over a temperaturerange of −20° C. to 50° C. The stretched polymer film may have a storagemodulus of 685.2 MPa at 25° C. Thus, an EMP actuator may be made bycasting a layer of EMP polymer (e.g., a P(VDF-TrFE-CFE) orP(VDF-TrFE-CTFE) terpolymer).

The stretched EMP film may be metallized by sputtering gold on bothsides of the film. Various voltages were applied to the resulting EMPactuator and the changes in film length in the direction parallel tostretching were measured. The stretched EMP film has strain S₁ of 0.48%at 40 MV/m and 2.1% at 100 MV/m.

Table 1 shows the performance of actuators made with modified,P(VDF-TrFE)-based EMP (‘EMP”), dielectric elastomer and piezoceramics.

Elastomer Piezoceramics Property EMP DEAP (PZT 5H) Strain (Stretching2.0% at 100 5-10% at 100 0.1% at 2 Direction) V/μm V/μm V/μm Young'sModulus (MPa) >500 ~1 ~100,000 Vibration Mechanical >0.1 ~0.005 ~0.05Energy Density (J/cm³) Dielectric Constant 35 3 2500 Dielectric Loss (%)5 5 2 Minimal Film Thickness 3 18 50 (μm) Voltage for Listed Strain 3001800 100 Operating Temperature −20° C.~ −20° C.~ −50° C.~ 50° C. 50° C.100° C. Response Time (ms) <1 <10 <0.1

As shown in Table 1, an EMP layer made with modified, P(VDF-TrFE)-basedEMP has balanced electromechanical response and mechanical modulus. Theoutput vibration mechanical energy density of such an EMP layer is alsosignificantly higher than the elastomer DEAP and piezoceramic actuators.

Each EMP actuator may be actuated independently or in concert with otherEMP actuators. As explained below, the EMP actuators may excitestructural modes of the haptic surface within a desired haptic frequencyband. Also, the EMP actuators may be arranged to operate as a phasedarray to focus haptic feedback to a desired location. In one embodiment,the EMP actuators may be laminated on a thin glass or plastic substratethat is less than 1,000 μm thick. Such a haptic surface is sufficientlythin to effectively transmit a haptic event without significantlyattenuating the actuator output. Suitable substrate materials includetransparent materials such as glass, polycarbonate, polyethyleneterephthalate (PET), polymethyl methacrylate, polyethylene naphthalate(PEN), opaque material such as molded plastic, or mixtures thereof.Other suitable substrate materials include multi-component functionalsheets such LCD, OLED, PET and combinations thereof.

EMP actuators disclosed herein may be actuated by low driving voltagesof less than about 300 volts (e.g., less than about 150 volts). Thesedriving voltages typically may generate an electric field of about 40V/um or more in the EMP layer of the EMP actuator. The EMP actuators maybe driven by a voltage sufficient to generate an electric field that hasa DC offset voltage of greater than about 10 V/μm, with an alternatingcomponent of peak-to-peak voltage of less than 300 volts. (Theexcitation signal need not be single-frequency; in fact, an excitationsignal consisting simultaneously of two or more distinct frequencies maybe provided.) The EMP actuators disclosed herein provide a hapticvibration of substantially the same frequency of frequencies as thedriving voltage. When the driving voltages are in the audio range (e.g.,up to 40,000 Hz, preferably 400-10000 Hz), audible sounds ofsubstantially those in the driving frequency or frequencies may begenerated. These EMP actuators are capable of switching betweenfrequencies within about 40 ms, and are thus suitable for use in HDhaptics and audio speaker applications. The EMP actuators are flexibleand can undergo significant movement to generate high electrostrictivestrains. Typically, a surface deformation application would useexcitation frequencies in the range between 0-50 Hz, a localized hapticapplication would use excitation frequencies in the range between 50-400Hz, and an audio application would use excitation frequencies in therange between 400-10,000 Hz, for example.

When driven under an AC signal, the waveform may be triangular,sinusoid, or any arbitrary waveform. In fact, the waveform can becustomized to generate any specific, desired tactile feedback. Forexample, the frequency of the waveform can be the same throughout theduration of a haptics event, or may be continuously changed. Thewaveform or the amplitude of the AC signal can also be the samethroughout the haptics event, or continuously changed.

The EMP actuators disclosed herein may have latency rise time (i.e., thetime between the EMP actuator receiving its activating input signal tothe EMP actuator providing the mechanical haptic response) from lessthan about 5 milliseconds up to about 40 milliseconds. The EMP actuatorsmay have a decay time (i.e., the time between the EMP actuator receivingthe cessation of the activating input signal to the EMP actuator'shaptic response falling below the user's detectable threshold) from lessthan about 5 milliseconds up to about 40 milliseconds. The EMP actuatorsmay have an acceleration response of greater than about 0.5 G to about2.5 G over a frequency range of about 100 Hz to about 300 Hz.

The above detailed description is provided to illustrate the specificembodiments of the present invention and is not intended to be limiting.Numerous variations and modifications within the scope of the presentinvention are possible. The present invention is set forth in thefollowing claims.

We claim:
 1. A two-sided keyboard comprising a first surface and asecond surface on opposite sides of the two-sided keyboard, wherein eachof said first and second surfaces include: a force-sensing layerincluding one or more force-sensing sensors; one or moreelectromechanical polymer (EMP) transducers to provide a localizedhaptic response to a force detected by the force-sensing layer; and acovering layer covering the force-sensing layer and the EMP transducers,wherein the EMP transducers are directly attached to an underside of thecovering layer such that the localized haptic response is transmitted tothe covering layer without going through an intervening passive layer.2. The two-sided keyboard of claim 1, wherein each of said first andsecond surfaces include a cushion attached to each EMP transducerbetween the EMP transducer and a corresponding one of the force-sensingsensors to which the EMP transducer is aligned, wherein the cushion hasa hardness between 20 A-30 A.
 3. The two-sided keyboard of claim 1,wherein the force-sensing sensors comprise a force-sensing resistormaterial.
 4. The two-sided keyboard of claim 1, further comprising aspacer layer provided between the covering layer and the force-sensinglayer, wherein the spacer layer has one or more cavities each alignedwith one of the force-sensing sensors, so as to accommodate acorresponding one of the EMP transducers.
 5. The two-sided keyboard ofclaim 1, wherein between the one or more EMP transducers and theforce-sensing layer is provided an air gap.
 6. The two-sided keyboard ofclaim 1, wherein each of the first surface and the second surface can beused independently as an input device.
 7. The two-sided keyboard ofclaim 1, wherein the two-sided keyboard is attached to a tabletcomputer.
 8. The two-sided keyboard of claim 7, wherein the both of thefirst surface and the second surface are used simultaneously for inputto the tablet computer.
 9. The two-sided keyboard of claim 7, whereinthe first surface and the second surface are used to cover the tabletcomputer.
 10. The two-sided keyboard of claim 7, wherein tablet computerhas a display and wherein the first surface faces the display, and thesecond surface faces away from the display, and wherein the secondsurface can be used to provide input to the tablet computer.
 11. Aportable computing device comprising: a tablet computer having a firstside, a second side, and a controller; and a two-sided keyboard having afirst surface and a second surface provided to cover the second side ofthe tablet computer, the two-sided keyboard having (i) a firstconfiguration wherein, the first surface of the two-sided keyboard isopened up for data input, and (ii) a second configuration wherein thetwo-sided keyboard rests flat against the second side of the tabletcomputer and provides the second surface of the two-sided keyboard fordata input, wherein each surface of the two-sided keyboard comprises: aforce-sensing layer including one or more force-sensing sensors; one ormore electromechanical polymer (EMP) transducers to provide a localizedhaptic response to a force detected by the force-sensing layer; acovering layer covering the force-sensing layer and the EMP transducers,wherein the EMP transducers are directly attached to an underside of thecovering layer such that the localized haptic response is transmitted tothe covering layer without going through an intervening passive layer.12. The portable computing device of claim 11, wherein each of saidfirst and second surfaces of the two-sided keyboard include a cushionattached to each EMP transducer between the EMP transducer and acorresponding one of the force-sensing sensors to which the EMPtransducer is aligned, wherein the cushion has a hardness between 20A-30 A.
 13. The two-sided keyboard of claim 11, wherein theforce-sensing sensors comprise a force-sensing resistor material. 14.The portable computing device of claim 11, wherein the two-sidedkeyboard further comprising a spacer layer provided between the coveringlayer and the force-sensing layer, wherein the spacer layer has one ormore cavities each aligned with one of the force-sensing sensors, so asto accommodate a corresponding one of the EMP transducers.
 15. Theportable computing device of claim 11, wherein between the one or moreEMP transducers and the force-sensing layer is provided an air gap. 16.The portable computing device of claim 11, wherein the both of the firstsurface and the second surface are used simultaneously for input to thetablet computer.
 17. The portable computing device of claim 11, furthercomprising a protective covering provided to cover the first side of thetablet computer, wherein the protective covering is configured to befolded to serve as a stand for propping up the tablet computer, andwherein only the first surface of the two-sided keyboard is used forinput to the tablet computer.
 18. A two-sided keyboard, the two-sidedkeyboard comprising: a first surface comprising: a first force-sensinglayer including one or more force-sensing sensors; a first set ofelectromechanical polymer (EMP) transducers to provide a localizedhaptic response to a force detected by the force-sensing layer; and acovering layer covering the first force-sensing layer and the first setof EMP transducers; and a second surface on a side opposite of the firstsurface, the second surface comprising: a second force-sensing layerincluding one or more force-sensing sensors; and a second set ofelectromechanical polymer (EMP) transducers to provide a localizedhaptic response to a force detected by the force-sensing layer.
 19. Thetwo-sided keyboard of claim 18, wherein each of said first and secondsurfaces include a cushion with a hardness between 20 A-30 A.
 20. Thetwo-sided keyboard of claim 18, wherein the both of the first surfaceand the second surface are used simultaneously for input to the tabletcomputer.